1. Field of the Invention
The invention relates to the field of implantable medical device systems and, more particularly, to systems and methods to improve the efficiency or speed of adjusting or “optimizing” the gain settings of the implantable medical device systems for individual patients.
2. Description of the Related Art
Implantable medical device systems have been developed to treat a wide variety of patient health ailments. One particular type of implantable medical device system includes implantable pacemakers and implantable cardioverter-defibrillators (ICDs) which are configured to automatically monitor the patient and selectively provide appropriate therapy for a variety of cardiac arrhythmias. Implantable cardiac stimulation devices, such as pacemakers and/or ICDs are available in a wide variety of configurations and are typically further individualized for the particular needs of a given patient. This is typically implemented by selecting an appropriate configuration of implantable cardiac stimulation device for the patient and further customizing that particular configuration by programming a plurality of operating characteristics or parameters of the device.
Programming of the device typically initially takes place in a clinical setting where a physician implants the device, affixes one or more patient leads, and performs an initial programming of the device. This procedure is typically assisted by other attending clinical personnel as well as with a physician's programmer which establishes telemetric communication with the device being implanted. The programmer allows the clinician to communicate with the device both for providing programming and other data commands as well as to interrogate the device, for example to extract data indicative of the device's performance and configuration. As may be expected with a relatively complex medical therapy system, a number of parameters or operating characteristics must generally be set, verified, evaluated, and frequently adjusted. One particular type of operating characteristic or parameter which generally needs to be individually adjusted for the particular patient and device are amplifier gain settings.
Amplifiers typically have a dynamic range and in implantable medical device applications, this dynamic range is generally adjustable. In general, the dynamic range of amplifiers is preferably adjusted to employ a substantial portion of the available dynamic range of the amplification, however, also adjusted to avoid saturation of the amplifier. Employing a substantial amount of the dynamic range available improves the discernable resolution of the amplified signal which facilitates more precise evaluation of a sensed signal. Saturation of the amplifier is preferably avoided as during periods of saturation, the magnitude of the amplified signal is no longer proportional to the input signal.
Saturation occurs when the amplifier can no longer provide a proportional amplified signal as the output of the amplifier reaches a maximum output value.
The amplitude multiplication or amplification factor of the input signal provided by the amplifier is referred as the gain. When the amplitude of the input signal multiplied by the current gain exceeds the maximum amplifier output, amplifier saturation occurs. Thus, the gain would be adjusted lower for a given input signal to bring the amplification of the input signal within the available maximum amplifier output so to fit within the available dynamic range. This is also referred to as adjusting the sensitivity of the system. System sensitivity is the complement of gain of the amplifier, e.g. an increase in sensitivity corresponds to a decrease in gain.
This process of adjusting the gain of an amplifier to employ a substantial portion of the available dynamic range while avoiding saturation conditions is generally referred to in the field as “gain optimization.” As used herein, the terms “optimization” or “optimizing” are terms of the art and refer simply to a process of evaluating and adjusting or individualizing the operating parameters of an amplifier system for improved sensing of the expected signals. Optimizing or optimization does not imply that this process results in a perfect setting for the system or that further improvements are not available. Thus, optimizing and optimization are to be interpreted as relative terms and not as absolutes.
In particular, as signals frequently provided to the amplifiers for amplification are of a physiologic origin, they are subject to variation that is frequently subject to change on a cycle to cycle basis, on a diurnal basis, and on an aperiodic or unpredictable basis. It is thus frequently preferable to provide at least some safety margin in the setting of the dynamic range to accommodate unusually low or high input signal levels. Gain optimization in the context of sensing physiologic signals is a matter of compromise and balancing multiple factors to achieve improved, but not necessarily perfect performance.
A gain adjustment or optimization procedure generally proceeds in an interactive manner with the physician throughout a process of iterative adjustment of the gain settings and observation and analysis of the adjusted amplification output. A typical procedure for evaluating and adjusting or optimizing the amplifier gain for a particular patient and device typically encompasses an interval of 20-30 seconds up to several minutes. This constitutes “dead time” for the attending clinician as limited other aspects of the programming of the device can generally take place while the gain optimization procedure is being conducted. As physicians and other clinical personnel are highly trained and compensated personnel, it is desirable that efficient use be made of their time during the implantation procedure. Physicians have reported frustration with extended durations of gain optimization procedures as they are in many existing implementations effectively forced to wait until the gain optimization process concludes before proceeding with further tasks in the initial implant and programming procedure.